Higher alkyl acid ester production



Patented Jan. 11 1944 HIGHER ALKYL ACID ESTER PRODUCTION Anton Johan Tulleners, Long Beach, Calii'., as-

slgnor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application January 30, 1942, Serial No. 428,871

4 Claims. (Cl. 260-460) This invention relates to the manufacture of alkyl acid esters having an alkyl group of at least seven carbon atoms. proved procedure whereby such esters may be produced more economically than was heretofore possible. The invention is especially concerned with a more advantageous method of selectively separating free acid from mixtures comprising such acid and higher alkyl acid esters.

The higher alkyl acid esters, such for example as mono-alkyl sulfates, monoand di-alkyl phosphates, mono-alkyl borates and the like, are produced by reacting oleflnes or aliphatic alcohols having at least seven carbon atoms per molecule with a polybasic inorganic acid, preferably of at least 80% concentration. As normally carried out these reactions result in the formation of a mixture of free acid and alkyl acid ester from which any neutral alkyl esters and/or unreactedhydrocarbons separate relatively easily. The free acid does not separate readily from the alkyl acid esters, however, and is an undesirable component of the product not only because it represents a loss of useful reagent but also because it may lead to side reactions of the alkyl acid esters during subsequent treatment. It has been proposed to reduce such undesirable side reactions by careful control of th temperature during dilution and/or neutralization of the alkyl acid ester containing mixture. Such control is diflicult and at best inadequate to completely. suppress side reactions such as hydrolysis or 'decomposition of the acid alkyl' esters during dilution or neutralization so maximum yields'of desired products are not obtained. In United States Patents 2,078,516 and 2,155,027 I have described and claimed improvements over such methods of operation, more particularly procedures for selectively separating free acid from such mixtures by means of aqueous solvents. While these procedures represent a marked advance over prior methods of operation, especially in that higher yields of acid alkyl esters of higher purity may be obtained thereby and a material saving taxes of the previous methods. It may be used in lieu of, or preferably in combination with, the

It deals with an improcess of either or both of the aforementione patents.

The invention may be applied to the separa tion of a wide variety of inorganic acids iron higher alkyl acid esters of all types. Typical o the acid esters which maybe present in the mix tures treated are the primary, secondary and ten tiary octyl,nonyl,decy1, dodecyl, tetraand hexadecyl, acid sulfates, phosphates and borates am the corresponding dialkyl phosphates, borates, etc, as well as mixed esters of such tribasic acids containing, for example, methyl, ethyl, isopropyl or butyi ester groups in combination with one of the foregoing higher alkyl ester groups. Substitution products of such esters may also be used as well as the homologues and analogues of the esters listed by way of example. Among the difierent acids which may be separated from such acids are, for example, not only the corresponding free acids but also other acids such as benzene sulphonic acid and the like. For the purpose of affording a clear understanding of the invention, but without imposing any limitation thereon, it will be described with more particular reference to the treatment of the mixtures of acid alkyl esters and free acids formed by absorbing olefines having eight or more carbon atoms per molecule in polybasic inorganic acids, particular- 1y sulfuric acid, which mixtures are commonly referred to as acid liquors." It will be understood, however, that mixtures of higher alkyl acid esters and free acids of other types and/or sources may be similarly treated. Thus esteracid mixtures obtained a intermediates in processes such as are described in United States Patents 2,139,394 and 2,152,292 may be used.

The invention is based upon the discovery that free acid can be separated from alkyl acid esters without dilution of the mixture. This separation is most preferably effected by centrifugation. One suitable method of carrying out the process as applied to the production of acid sulfates from oleflnes comprises contacting the oleflne-containing hydrocarbon with-sulfuric acid, for example of concentration, preferably using a stoichiometric excess of acid based on the olefine employed. The reaction may advantageously be carried out in a tower to which the oleflne containing hydrocarbon is fed at the bottom and the sulfuric acid at the top while the mixture is constantly agitated as by means of a stirrer. The

sulfation product substantially free from unreacted hydrocarbon may then be withdrawn from the bottom of the tower and passed to a centrifuge which is operated so as to separate unfrom the higher alkyl acid esters may be elected reacted sulfuric acid from the higher alkyl acid sulfates present therewith. The acid recovered in this way will be only slightly more dilute than that used initially for reaction with the oleflne and will be substantially free from alkyl esters so that it constitutes valuable material for. re-

. use in the process.

It has already been proposed to use centrifugation for various steps in the production of alkyl esters. Thus the centrifugation of reaction products of olefines with inorganic acids such as 8111-- admixtures with alkyl acid esters without substantial dilution of the mixture with aqueous agents prior to the separation.

. The process of the invention may be conducted in other ways than that described in the foregoing illustrative example. Instead of countercurrent treatment of the define-containing hydrocarbon in a tower, the reaction may be carried out by concurrent flow of acid and hydrocarbon or the two liquids may be agitated in a stirring vessel, or pumped through a coil or time tank at a rate sufliclent to insure adequate mixing. United States Patents 1,967,410 and 2,106,- 521,,for example, describe methods which" are especially advantageous for reacting oleflnes with inorganic acids.

The unreacted hydrocarbon is preferably separated from the reaction mixture before removing the free acid from the acid alkyl esters according to the invention. The hydrocarbon sepacid, they may be advantageously used in such subsequent washings.

The process may be applied to the purification of a wide variety of higher alkyl acid esters conaration maybe efl'ected by decantation or centrlfugal separation or in any other suitable manner. In some cases it may be found more desirable to postpone the hydrocarbon separation. until after the separation of free acid. Where actions may take place, is thereby avoided. Solvents for the higher alkyl acid esters, which solvents are substantially immiscible with the acid, may be used to promote the separation of the free acid. Typical solvents which may be thus used are, for example, ketones having about six to fifteen carbon atoms per molecule, such as methyl hexyl 'ketone, ethyl cyclohexyl ketone, mesityl oxide, benzophenone, etc., and esters as octyl acetate, ethyl butyrate, methyl benzoate, and the like, as well as suitable hydrocarbons or substitution products, for example chlorination products, of any of these compounds. The free acid recovered in the separation step may be returned for further reaction with the olefinic hydrocarbon or may be used for other purposes. Batch, intermittent or continuous methods oi? carrying out the free acid separation may be em-- ployed.

If desirable, further separation of free acid taming free acid regardless of the source of the mixture. Thus, for example, mixtures of higher alkyl-acid esters and acids which are different from that used in the production of the esters may be treated.

The following example illustrates one method of carrying out the process of the invention and shows the advantages obtainable thereby.

A vapor phase cracked distillate of 160 C. to 300 C. boiling range was reacted with 90% sulfuric acid using'l i mols of acid per mol of olefine as calculated from the bromine number of the cracked distillate. ,The acid and olefine were reacted in a tower into which the cracked distillate was red at the bottom and the acid at the top while intimate contact between the phases was assured by agitating the mixture by. means of a motor driven stirrer. 'The sulfation product leaving the tower was passed to a centrifuge operated at about 900l200 R. P. M. which efiected a clean separation of sulfuric acid of 84% concentration. The alkyl acid sulfates thus partially freed of sulfuric acid were fed to a mixer to which 3% by weight of water was added. The diluted mixture was then passed to the next centrifuge from which sulfuric acid of 65% concentration, and a sulfation product substantially freed of free sulfuric acid were run oil. When the latter was worked up to sodium salts of the alkyl acid sulfates the latter were obtained in a yield of about 80% by weight based on the cracked distillate used.

The recovered 84% sulfuric acid can be fortifled with technical sulfuric acid of 96% concentration and re-used in the suliation step without recourse to concentration. The 65% sulfuric acid recovered by the washing treatment may be re-concentrated and similarly reused or may be applied in pre-treating the oleflnic feed to remove impurities or for other refining purposes.

It will be seen that the process of the invention ofiers many advantages over prior methods of operation, particularly with respect to economy and emciency, and that it facilitates further working up of the recovered alkyl acid esters so that high yields of desired final products may be readily obtained. It will also be clear that the process is applicable to the separation of a wide variety of esters and acids and that the operating conditions and procedure may be widely varied. Consequently, the invention is not to be limited to the details of operation disclosed by way of illustration and example, nor by any theory suggested in explanation of the improved results obtained.

I claim as my invention:

Lin :2. process of producing a higher alkyl acid ester wherein an olefin having at least seven carbon atoms per molecule is reacted with a polybasic inorganic acid of at least 80% concentration and a mixture of free inorganic acid and an alkyl acid ester thereof is obtained, the improvement which comprises centrifuging said mixture without reducing the concentration of the free acid content to separate therefrom free acid substantially free from alkyl acid esters, and separately recovering the separated free acid and alkyl acid ester.

"2. In a process of producing a higher alkyl acid ester wherein an olefin having at least seven car on atoms per molecule is reacted with a polybasicstinorganic acid of at least 90% concentratiofi and a mixture of free inorganic acid and an alkyl acid ester thereof is obtained, the improvement which comprises subjecting said mixture without reducing the concentration of the free acid content to the action of a centrifugal force suificient to separate therefrom a phase comprising .free acid substantially free from said alkyl acid ester for'a period at which substantial separation of said acid phase is effected and separately recovering the separated free acid and an alkyl acid ester at least partially freed of said acid.

3. In a process of producing a higher alkyl acid sulfate by reacting an alcohol having at least seven carbon atoms per molecule with a stoichiometric excess of sulfuric acid of at least 80% concentration, the improvement which comprises centrifuging the resulting mixture of free sulfuric acid and alkyl acid sulfate to effect separation of free acid from said acid sulfate without reducing the concentration of said free sul-I furic acid, separately withdrawing the separated acid, and returning at least a part thereof to said reaction without removing water therefrom.

4. In a process of producing a higher alkyl acid sulfate by reacting hydrocarbon containing an olefin of at least seven carbon atoms per molecule with sulfuric acid of at least 80% concentration, the improvement which comprises centrifuging the resulting mixture of free sulfuric acid and alkyl acid sulfate to effect separation of free acid from said acid sulfate without reducing the concentration of said free sulfuric acid, separately withdrawing the separated acid, and returning at least a part thereof to said reaction without removing water therefrom.

ANTON JOHAN TULLENERS. 

